In theory, bipolar batteries can be used to improve battery energy storage capacity on a weight and volume basis, to reduce packing weight and volume, to provide stable battery performance and low internal resistance.
A bipolar battery construction comprises an electrically conductive bipolar layer, so called biplate, that serves as electrical interconnection between adjacent cells in the battery as well as a partition between the cells. In order for the bipolar construction to be successfully utilised, the biplate must be sufficiently conductive to transmit current from cell to cell, chemically stable in the cell's environment, capable of making and maintaining good contact to the electrodes and capable of being electrically insulated and sealable around the boundaries of the cell so as to contain electrolyte in the cell.
These requirements are more difficult to achieve in rechargeable batteries due to the charging potential that can accelerate corrosion of the biplate and in alkaline batteries due to the creep nature of electrolyte. Achieving the proper combination of these characteristics has proven very difficult. For maintenance-free operation it is desirable to operate rechargeable batteries in a sealed configuration. However, sealed bipolar designs typically utilise flat electrodes and stacked-cell constructions that are structurally poor for containment of gases present and generated during cell operation. In a sealed construction, gases generated during charging need to be chemically recombined within the cell for stable operation. The pressure-containment requirement creates additional challenges in the design of a stable bipolar configuration.
Battery manufacturers have not developed bipolar batteries commercially because a working seal design has always been a problem. The vast majority of development work to date has been strictly related to lead/acid technology. The seal is difficult to achieve due to the galvanic creepage of the electrolyte, the corrosive conditions and the heat and pressure generated by the battery. Other manufacturers have tried to make leak-proof seals, and use rigid approaches that ultimately fail due to thermal expansion and pressure changes. In the subject disclosure, the leakage has been separated into two components: electrolyte leakage and gas leakage. A hydrophobic barrier is used in conjunction with a starved electrolyte condition to prevent electrolyte from reaching the pressure seal. The pressure seal is flexible and designed to move with the biplate.
Bipolar batteries have the theoretical advantage to improve battery energy storage efficiency, with reduced weight, volume and cost. The bipolar approach is simple in concept, with both a direct, uniform and short current path, and a minimum number of parts which allow ease of assembly. Despite these potential advantages, there are no bipolar batteries commercially produced at this time. A review of patent applications reveals many patents on lead acid designs. There are only a few for Nickel based battery systems (e.g. DE 198 381 21 by Deut Automobil GmBH)
New requirements in the field of transportation, communications, medical and power tools are generating specifications that existing batteries cannot meet. These include higher cycle life and the need for rapid and efficient recharges.
NiMH systems are seen as the alternative to meet cycle life, but costs for existing conventional fabrication are too high.
There is a need for a battery that offers high power charge and discharge capability with long life at affordable prices.